Gonadotrophic control of steroidogenesis in human granulosa-lutein cells

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Abstract
Granulosa-lutein cells were harvested from periovulatory follicles in human ovaries and cultured for up to 6 days, equivalent to almost half of a normal luteal phase. The average rate of basal progesterone accumulation in the culture medium was constant at .apprx. 36 nmol progesterone/106 cells/day. Oestradiol accumulation was too low to measure in the absence of precursor androgen. Basal aromatase activity (measured as oestradiol formed in 3 h from 10-6 M exogenous testosterone) was high (average 1.15 nmol oestradiol/106 cells/ 3 h) at the time of cell isolation (Day 0) but fell by > 90% on Day 1. By Day 2 the activity had partly recovered and averaged 62% of the Day 0 value, rising to 70% on Day 6. This loss and recovery of aromatase activity was independent of the addition of gonadotrophic hormones to the culture medium. However, dose related increases in aromatase activity occurred in the presence of highly pure human pituitary LH (0.1-30 ng/ml). The increase was observed on Day 4 and was maximal on Day 6 (average 3-fold increase over control) in the presence of LH concentrations .gtoreq. 1.0 ng/ml. LH also caused dose-related increases in progesterone accumulation by Day 4 with maximal stimulation on Day 6 (avergage 3-fold increase over control) at .gtoreq. 10.0 ng/ml. Dose-related stimulation of aromatase activity by human pituitary FSH also occurred but maximal stimualtion required the presence of 300 ng FSH/ml and progesterone accumulation was hardly affected at this dose. Small contaminating amounts of LH in the FSH preparation (.apprx. 0.5% on a mass basis) may have caused this stimulation but a specific FSH action was not ruled out. These results demonstrate time-related changes in steroidogenic potential with enhanced sensitivity to LH as human granulosa-lutein cells age in culture. Since fully luteinized granulosa cells retain an LH-responsive aromatase system, they may play a central role in LH-controlled oestrogen biosynthesis in the corpus luteum.